The ability of a swab cup to pick up light loads as well as heavy loads depends upon the cup's ability to deform in accordance with the operating load conditions. For light load operation, the swab cup must deform with less force or fluid weight acting on the cup than is present during heavy load operation. In light load operation, the swap cup's upper portion must deform under the light weight load to contact the tubing interior wall so the swab cup can pick up and transport well fluid in the tubing. In heavy load operation, the upper and the lower portions of the swab cup must deform to carry the heavier load and circumferentially expand the swab cup to seal against the tubing interior so the swab cup can transport the well fluid without leakage.
In prior swab cup constructions, those having single length wire reinforcing members, have a tendency to be rather stiff thus do not pick up or retain the lighter loads. Some prior swab cup constructions have two lengths of wire reinforcing members and additionally have an elastomeric lip extending substantially beyond the wire reinforcing members to seal in very light loading conditions. While this later construction may pick up light loads of well fluid, it is a significantly longer swab cup than the others and is prone to damage of the unsupported or unreinforced upper portion of the swab cup body.